David & Laurie,

Remember that cats do not need to be social creatures - unlike the
pack-orientated dog; they function happily on their own without a social
structure around them. They are unlikely to feel the 'need' for a companion
even though you would wish to have another cat around. You cannot force cats
to like each other - some will live with a newcomer easily, others will
never relate, or they may just manage to live alongside each other in an
uneasy truce - you can only try. However, if there is no competition for
food or safe sleeping places then cats will accept each other eventually and
some will even seem to form close bonds with one another. While it may be a
matter of feline choice as to whether cats relate, how you introduce a new
cat or kitten into your home and to a resident cat or cats can make the
difference between success and failure. Once a relationship becomes violent
or very fearful and the cat feels threatened, it can be very difficult to
change the behavior patterns. Thus, careful introductions which prevent
excessive reactions and take things slowly are vital. So far from your
description of how you introduced the kitten to the cat, you have done
everything correct. Either it accepts the kitten or it doesn't. You can't
force the relationship. You need to give it more time. If in a few weeks or
a month the same behavior is happening, you may have a problem. There are
allegedly tricks that you can use to help accommodate all the cats, such as
alienating the kitten in another room with a door. This way the other cats
cannot harm the kitten and get use to the scent of another cat. Another is
showing little to no affection to the kitten and reinforcing the other two
cats with petting and treats. Those suggestions may work, but for me I just
let the cats come together on their own. Remember, you are dealing with
cats, not tiger cubs.

Give it a least a month...it takes time...
The hissing and swatting is very normal behavior and is a way of them
establishing thier boundries...

Its important that you give your two older cats attention so they know
that you  have not abandened them..PLUS its important that they see you
pet and show affection with the kitten. that way THEY know you accept
the kitten...

I got a new kitten myself back in Sept. and have two older cats as
well...It has taken a few weeks but they are all becoming quiet friendly
to the point that the middle cat and the kitten will even sleep next to
each other

Be patient. Show love and affection to all three in the presences of all
three...If one of them shows some  timidity the also give them some love
and affection in private where they feel and know they are safe with you...